Several systems have been proposed to implement intermodal transfer over long distances as a commercially viable alternative to wholly road freight services which are available. Such systems include "piggy back" transport of road semi-trailers, complete lorries, or other land-moving vehicles on conventional railroad flat cars of sufficient length to support the length of one or two of such vehicles or containers.
The cost advantage enjoyed by long distance rail transportation of semi-trailers and the like on railroad flat cars is well known and recognized by industry. It has been recognized, however, that there are inefficiencies inherent in the basic concept of transporting semi-trailers or the like on railway flat cars for shorter distances, i.e., less than 500 miles.
The inability of railroads to effectively compete in a shorter distance market stems from two factors. The first factor involves the problem of matching the lengths of the semi-trailers to the flat cars. Although flat cars are available in lengths ranging from 40 feet to 90 feet and more, a fairly significant number are in the 80 to 90 feet range. Semi-trailers are also available in a variety of lengths, but a significant number are in the 40 to 50 feet range. Thus, it is fairly common that semi-trailers must be transported one on one because they are too long for double, tandem loading on available flat rolling stock. Thus, except where the railroad flat cars are matched with semi-trailers either approximately equal to or approximately half their lengths, piggy back transportation of semi-trailers tends to be somewhat inefficient because relatively large amounts of space are wasted and unoccupied in one-on-one loadings.
The second problem concerns the prohibitive capital costs and operating expenses associated with the loading of trailers on today's railroad flat cars. Because of terminal costs associated with loading and unloading the trailers on flat cars, railroads find it difficult to absorb such terminal costs while remaining competitive with road freight services.
U.S. Pat. No. 4,653,966, assigned to the same assignee as instant application, discloses a unique system for transporting highway semi-trailers, or the like, by rail. Such system uses improved rail bogies as the sole support of adjacent rear and front ends of the trailer and as the sole connecting means between such trailers, to form trains.
The patented system includes a rail bogie having a frame structure supported on wheeled axles positioned at the respective ends of the frame structure. The frame structure defines a pair of end deck surfaces positioned above the wheeled axles and a central drop deck surface disposed between and below the end deck surfaces. A fifth wheel assembly is supported above each of the end deck surfaces for receipt of a kingpin of a semi-trailer. A deck plate member is pivotally secured to the drop deck surface for planar rotation with respect thereto about a substantially vertical axis. A pair of transversely spaced, longitudinally extending, internal and external rub rail members extend upwardly from the drop deck plate member for receipt of semi-trailer tandems therebetween.
As disclosed, the drop deck plate is movable between first and second positions. In one position, the rub rail members on the deck plate are substantially parallel to the longitudinal axis of the frame structure. When in its second position, the rub rail members on the deck plate member are substantially perpendicular to the longitudinal axis of the frame structure.
In accordance with that system, a semi-trailer extends between a pair of adjacent bogies. The tandems of the trailer are received and supported on the drop deck plate between the corresponding rub rail members of a first bogie and the kingpin of the trailer is received and supported on the fifth wheel assembly of the immediately adjacent bogie. The procedure for loading and unloading the semi-trailers onto and from the bogies is facilitated by the rotating drop deck plate.
The system as disclosed in U.S. Pat. No. 4,653,966 has improved upon the prior system in that it allows for the straddling of a semi-trailer between two bogies or short flat cars, thus permitting the trailer frame rails to distribute longitudinal stress. Also, this system provides a timely procedure for loading and unloading the semi-trailers onto and from the bogies.
This system, however, is limited in its ability to secure a semi-trailer against endwise displacement relative to the deck plate member. Separate devices need to be provided to secure the semi-trailer tandems relative to the deck plate. Should such securement devices become dislodged during transportation, a trailer may be allowed or permitted an unwanted freedom of movement relative to the deck plate.